Analysis of Causes for the Severe Mixed Pollution Process in Yangquan City from March 19 to 25,2023

Ma Xingfen; Wang Yan; Yan Shiming; Wang Yunjian; Jia Liting; Mu Changjun

doi:10.16765/j.cnki.1673-7148.2025.04.010

Abstract：From March 19 to 25,2023,a mixed heavy pollution weather process with the strongest intensity and widest influence in the past three years occurred in Yangquan City,Shanxi Province.Through analyzing the air quality data,meteorological monitoring data,microwave radiometer data,and backward trajectory during this period,the backward trajectories are clustered by means of the binary K-means algorithm.The results show that:(1)This heavy pollution process is divided into three stages:from the haze stage to the sand-dust stage,and then to the sand-dust to haze stage.The first stage was the haze weather stage,affected by static-stable weather with low surface wind speed.The second stage was the stage of sand-dust weather,affected by the Mongolian cyclone that moved eastward and south-ward,causing the PM10 concentration to increase explosively.The third stage was the sand-dust to haze stage,which was affected by reflux weather.During this stage,the surface wind speed was reduced,the PM10 in the atmosphere gradually settled down as the result of gravity,making the PM2.5 gradually accu-mulate again.(2)The transport paths of pollutants during this heavy pollution process are divided into three categories.Spatially,the pollutant transport path in haze weather was first downward and then up-ward in the vertical direction.In terms of the pollutant transport speed,the moving speed of sand and dust was higher than that in the haze weather.(3)When the mixed pollution weather appeared in spring,the surface situation of haze weather was mostly saddle-shaped field,warm low-pressure type and high-pressure rear type,and the upper situation was mostly flat zonal circulation.The surface situation of sand-dust weather was mostly the high-pressure front(bottom)type,and the upper situation was mostly the meridional circulation with large gradient.(4)The concentrations of gaseous pollutants(SO2 and NO2)were greatly affected by the near-surface wind field,presenting different characteristics in the peri-od of dust and haze weather.(5)Below the height of 3.0 km,the temperature profile and water vapor density profile data in the boundary layer can make up for the lack of local conventional radiosonde data.Moreover,according to the temperature profile in the boundary layer,the ground inversion can be ob-served in advance.